This invention relates to an optical element and to an optical arrangement which comprises this type of optical element. The invention can be used in connection with the microlithography used in the production of microelectronic circuits. It therefore further relates to a lens barrel which is particularly suitable for use in a microlithography device and a microlithography device comprising this type of lens barrel.
For a plurality of optical applications, particularly however in the field of the aforementioned microlithography, it is necessary to position the optical elements used, for example lenses or plane-parallel plates, with the greatest possible accuracy within the space. In particular several of these optical elements must generally be positioned here relative to one another with corresponding accuracy. Due to the ever progressive miniaturisation of the microelectronic circuits to be produced, there is a constant need to increase the resolution of the optical systems used during production.
With increased resolution, the requirements for the accuracy of the optical elements themselves used also, among other things, become more stringent. This must be maintained as far as possible in the mounted state over the whole period of operation. It is particularly necessary here also to hold the optical element with as little stress as possible during operation in order to avoid image errors as a result of deformation of the optical element. Furthermore, in this context, it is necessary to achieve the most favourable dynamic behaviour possible of the optical system used with the highest resonant frequencies possible.
In order to achieve holding of this type of optical element with a small amount of stress, it is known from US 2002/0163741 A1 to hold a lens by means of three holding elements disposed on an annular frame. These holding elements respectively grab a ledge extending around the circumference of the lens and having contact surfaces disposed perpendicularly to the optical axis. The respective holding element clamps the ledge in the direction of the optical axis by means of the contact surfaces in two regions spaced apart from one another in the circumferential direction. In order to avoid the introduction of deformations of the frame via the two clamping regions spaced apart from one another into the lens, a mounting of the holding element on the frame is provided which provides corresponding degrees of freedom.
This design has, on the one hand, the disadvantage that a comparatively expensive mounting is required for the respective holding element. On the other hand, for the production of the contact surfaces a comparatively large region of the lens has to be processed with correspondingly high cost in order to ensure sufficient precision of the contact regions.
Furthermore, from DE 101 39 805 C1 a holder for a lens is known wherein three holding elements distributed around the circumference of the lens radially engage a V-shaped annular groove extending around the circumference of the lens. These holding elements lie against the lens with a certain pre-stress and in this way hold it, both, in the direction of the optical axis and in the circumferential direction and in the radial direction. The defined pre-stress is achieved here by the design of one of the holding elements being resilient in the radial direction.
This design too has the disadvantage, on the one hand, that for the circumferential V-shaped annular groove a comparably large region of the lens must be processed with correspondingly high cost in order to ensure that there is sufficient precision of the contact regions. A further disadvantage of the design is the fact that, on the one hand, it is only suitable to a certain extent for thin lenses, and on the other hand, increased production expenditure is required due to the risk of fractures on the lens.
Therefore, the objective which forms the basis of this invention is to provide an optical element and an optical arrangement of the type specified above which does not have the aforementioned disadvantages or at least only has them to a lesser degree, and in particular enables holding with as little stress as possible at simple producibility.